Nine point corneal thickness measurements and keratometry readings in normal corneas using ultrasound pachymetry.

Central, paracentral, and peripheral corneal thickness measurements using ultrasound pachymetry and keratometry readings were performed in 303 normal corneas. The mean central corneal thickness was 515 +/- 34 microns (standard deviation) ranging from 410 to 625 microns. Mean paracentral thickness measurements ranged from 522 +/- 40 microns inferiorly to 574 +/- 41 microns superiorly; mean peripheral thickness measurements ranged from 633 +/- 50 microns inferiorly to 673 +/- 49 microns superiorly. Central corneal thickness measurements were not found to be correlated with age, however, paracentral and peripheral thickness measurements tended to become thinner with age. There was also a trend that central corneal thickness decreased as the average keratometry reading increased. These trends, however, were not statistically significant. The mean difference between right and left central corneal thicknesses was 25 microns, ranging from zero to 136 microns. No significant differences in corneal thickness or keratometry readings were found between males and females or right and left eyes. No differences in these measurements were found with regard to time of day, month of the year, or systemic medication use. We conclude that there is a wide range of corneal thickness centrally, paracentrally, and peripherally in normal corneas.

Reproducibility and variation of corneal thickness in different locations in the cornea as measured by an ultrasonic pachymeter.

Corneal thickness was measured in nine positions of nineteen normal eyes with an ultrasonic pachymeter. A standardized protocol was used to examine for intraobserver and interobserver variation, day to day variation, and time of day variation in the measurement of corneal thickness. No statistically significant difference was noted for most points in intraobserver, interobserver, day to day, or different time of day variation measurements. However, it was noted that central measurements of corneal thickness tended to be less variable (more reproducible) than paracentral (p = .0366) and peripheral (.0032) measurements. Paracentral measurements were less variable than peripheral measurements (p = .0323). While this was a small study, 95% confidence intervals were also calculated for each of the nine corneal positions where measurements were performed.

Linkage of posterior polymorphous corneal dystrophy to 20q11.

Posterior polymorphous dystrophy (PPMD) is an autosomal dominant disorder of the cornea that is clinically recognized by the presence of vesicles on the endothelial surface of the cornea. The corneal endothelium is normally a single layer of cells that lose their mitotic potential after development is complete. In PPMD, the endothelium is often multi-layered and has several other characteristics of an epithelium including the presence of desmosomes, tonofilaments, and microvilli. These abnormal cells retain their ability to divide and extend onto the trabecular meshwork to cause glaucoma in up to 40% of cases. A large family with 21 members affected with PPMD was genotyped with short tandem repeat polymorphisms distributed across the autosomal genome. Linkage was established with markers on the long arm of chromosome 20. The highest observed LOD score was 5.54 (theta = 0) with marker D20S45. Analysis of recombination events in four affected individuals revealed that the disease gene lies within a 30cM interval between markers D20S98 and D20S108.